SPECIAL PHYSIOLOGY. 129 



that they are all derived from previously existing parents or stocks, 

 by ova, germs, gemmules, buds, seeds, or spores. Spontaneous gener- 

 ation, which will be hereafter discussed, has not yet been proved to 

 occur in regard to any organic body, animal or vegetable. Organic 

 bodies go through a cycle of changes, both of form and composition. 

 They are nourished, grow, and are continually changing their sub- 

 stance and shape; they attain perfection, give rise to new indivi- 

 duals like themselves, and then die. No such cycle of change and 

 reproduction is observed in regard to any inorganic body. 



SPECIAL PHYSIOLOGY. 



THE ANIMAL FUNCTIONS. 



THESE, as already explained, are Motion; Sensation, common and 

 special; the Regulation of Movement; and the higher Psychical 

 functions. 



MOTION. 



All power of intrinsic self-movement, or spontaneous action, in man 

 and animals, depends either on muscular contractility, that particular 

 form of contractility possessed by a specially organized tissue, the 

 muscular tissue, or the so-called ciliary motion exhibited by the minute 

 vibrating organs called cilia, or on the less common and obvious actions 

 of contractile sarcodous cells, or still simpler masses of protoplasm. 

 General movements are impressed on living animal bodies as well as- 

 on dead ones, by the force of gravitation, and these movements enter, 

 as it were, into their various locomotive or other acts, especially in 

 progression, whether this be terrestrial, aquatic, or aerial. Gravita- 

 tion also influences the special movements of the limbs and other parts 

 of the living body. 



The physical force resulting from the recoil of the yellow elastic 

 tissue, which is so frequently employed in the animal economy, like- 

 wise assists in the intrinsic movements of many parts ; but this tissue 

 cannot properly be regarded as an original source of motion, for it 

 must first be extended before it can act, and this extension is accom- 

 plished either by gravity or by muscular effort. 



There likewise occur in certain fluids and tissues of the body, when 

 examined under the microscope, movements of a tremulous character, 

 named molecular movements, as in the fine particles or molecular basis 

 of the chyle, in pigment granules suspended in fluid, or in these or 

 other minute granules contained in the interior of cells. These move- 

 ments are purely physical, and may be observed with the microscope 

 in any very minute particles of dead matter sufficiently light to float 

 in a fluid. 



Still more recondite molar and molecular movements, of a physical 



